1. Field of the Invention
The present invention is related to stopping and resuming reproduction of video information from an optical disk having a compact disk size on which compressed video information and corresponding audio information are recorded (so-called a video CD (Compact Disk)). The video information and audio information, in case of transiently stopping reproduction and resuming later, automatically resumes reproduction from the stopped position.
2. Description of Related Art A known LD (Laser Disk) has a diameter of 30 cm provides an optical disk on which video information is recorded.
Video information with extended length, such as a movie or the like, is often recorded on this LD. Thus, it may be desired that while reproducing the movie or the like, reproduction be transiently stopped in the middle, and after that, to resume reproduction from the stopped position.
An LD player for reproducing this LD comprises a last memory function for storing, when transiently stopping the reproduced video information, an absolute address, which represents a record position on the optical disk from the beginning of the whole video information recorded on the LD, of the picture at the stopped point. Upon resuming reproduction, by using this stored absolute address, reproduction is resumed from the absolute address.
Recently, there is also a known so-called video CD on which video and audio information known (similar to that on the LD) is recorded on an optical disk having a CD size smaller than the above-mentioned LD.
In this video CD, since video information and audio information with 74 minutes nearly similar to the LD are recorded on an optical disk having CD size, the video information and audio information are recorded in respectively compressed states. The MPEG1 (Moving Picture Experts Group 1) method, which is a national standard for a method of compressing and accumulating video information, is employed.
Now, compression of video information using the MPEG1 method is schematically explained with reference to FIGS. 18A and 18B.
In generally continuous frames, frame pictures located before and after one frame picture are similar to each other and have a mutual relation between each other, in many cases. The MPEG1 method notes this point and generates, on the basis of a plurality of frame pictures, another frame picture existing between the plurality of frame pictures, by means of an interpolation operation based on a movement vector between the respective frame pictures and the like. In this case, when recording the next frame picture in a sequence, only information with respect to a difference and the movement vector between the above mentioned plurality of frame pictures are recorded. Accordingly, when reproducing, it is possible to refer to this vector and estimated difference data from the above mentioned plurality of frame pictures to thereby reproduce the another frame picture. As a result, it is possible to carry out compression of the video information.
The MPEG1 method uses a unit of GOP (Group Of Picture), as a minimum data unit from which a picture can be singly reproduced, without referring to other frame pictures. FIG. 18A shows an example of a plurality of frame pictures constituting one GOP. In FIG. 18A, one GOP is composed of 15 frame pictures. Among those frame pictures, a frame picture shown by a symbol [I] is referred to as an I picture (Intra-coded picture). This means a frame picture in which one frame picture can be perfectly re-constituted by its own information. And, a frame picture shown by a symbol [P] is referred to as a P picture (Predictive-coded picture). This is an estimation picture generated by decoding the difference from other pictures reproduced on the basis of an already decoded I picture or P picture. Further, a frame picture shown by a symbol [B] is referred to as a B picture (Bidirectionally predictive-coded picture). This is an estimation picture reproduced by using not only an already decoded I picture or P picture but also a future I picture or future P picture recorded on the optical disk. After an I picture and a P picture are decoded, a B picture is reproduced and inserted between them. In FIG. 18A, the estimation relation (interpolation relation) between the respective pictures (frame pictures) are indicated by using arrows.
The order of the respective pictures in FIG. 18A shows the original sequence of source pictures before being recorded on the optical disk. As shown in FIG. 18B, they are recorded on the optical disk with the I picture within and at the beginning of a GOP. This is arranged by considering the estimation relation between the respective pictures when decoding.
Further, when recorded on the optical disk, a GOP header is disposed at the beginning of each GOP. This GOP header is defined so as to record GSC (Group Start Code) representing the beginning of the GOP, and TC (Time Code) which is time information representing elapsed time from the beginning of the reproduction of the whole video GOP information.
Furthermore, when recorded, for each above mentioned picture, a (Picture Start Code) is recorded representing the beginning of a picture layer and a TR (Temporal Reference) is recorded representing the display sequence (a numerical indicia in FIG. 18A) from a first picture within the GOP in which each picture exists.
The above mentioned MPEG1 method is widely generalized as a first international standard for picture compression. By using this method, it is possible to record a dynamic picture with 74 minutes of video on one optical disk.
On the other hand, a function called PBC (Play Back Control) function has recently been developed for a video CD, and a player comprising the PBC function is sold on the market. This PBC function is implemented by data called PST (Play Sequence Descriptor) recorded on the video CD with other video information and audio information. This function reproduces the video information and audio information recorded on the video CD, in a sequence designated by a designer (author) who designs the video information and audio information irrespective of the recorded sequence. For this reason, a menu screen by which a user selects a picture to be reproduced, and a static picture and a dynamic picture of effectively playing the recorded video information and audio information are recorded on the video CD corresponding to the PBC function, with the above mentioned video information and audio information and PST.
By this PBC function, the video CD has various user access performances. The user can carry out a numeric operation of specifying a desirable picture by a numeral key to thereby reproduce the specified pictures picture. A default selection operation of pushing a selection key while viewing a displayed menu screen to select and reproduce the desirable picture is also possible. A multiple default selection operation in which a picture of jump destination (a picture reproduced by skipping a plurality of pictures from a presently viewed picture) is different at when the selection key is pressed, and the like may also be provided.
However, because video information is compressed in the video CD on which the video information is recorded by the MPEG1 method, it is impossible to record the absolute address at the stopped point (as in the conventional LD) to thereby resume reproduction from a picture corresponding to the absolute address. This results in a problem because stop and of video reproduction are impossible.
That is, in a video CD on which video information is recorded by the MPEG1 method, even if the above mentioned TC (Time Code) or TR (Temporal Reference) is stored as an absolute address at the stopped point, in a case where TC and TR correspond to the P picture or the B picture shown in FIGS. 18A and 18B, the reproduction picture can not be reproduced only by this P picture or B picture. That is, as mentioned above, the P picture or the B picture data cannot by itself reproduce a complete picture frame corresponding to the P picture or B picture unless using I picture or P picture reproduced before that point. Accordingly, reproduction stopping and resumption using an absolute address as a conventional LD can not be used for a video CD.